Radio frequency keying pulse in electronic organ

ABSTRACT

A radio frequency signal is placed on the pickup bus of an audio-keyed electronic organ. The connection is through a resistor and capacitor which form with the input resistors of the audio switches a voltage divider, whereby the level of radio frequency voltage on the bus changes upon closure of any key switch. The radio frequency is amplified and applied to a rectifier to produce a DC potential proportional to the level of the radio frequency, and this is applied through a capacitor to a utilization circuit. Hence as the DC level changes through the capacitor, it appears as a pulse or spike at the utilization circuit, and this pulse or spike is used to key rhythm or other accompaniment effects.

United States'Patent [72] Inventors Harold O. Schwartz;

Anthony C. Ippolito, North Tonawanda, N.Y

[21] Appl. No. 867,742

[22] Filed Oct. 20, 1969 [45] Patented May 18, 1971 [7 3] Assignee The Wurlitzer Company Chicago, Ill.

[54] RADIO FREQUENCY KEYING PULSE IN ELECTRONIC ORGAN 22 Claims, 8 Drawing Figs.

[56] References Cited UNITED STATES PATENTS 5/1967 Heame 4/1967 Boenning 3,511,917 '5/1970 Mallett Primary Examiner-Milton O. Hirshfield Assistant Examiner-B. A. Reynolds Attorney-Olson, Trexler, Wolters & Bushnell ABSTRACT: A radio frequency signal is placed on the pickup bus of an audio-keyed electronic organ. The connection is through a resistor and capacitor which form with the input resistors of the audio switches a voltage-divider, whereby the level of radio frequency voltage on the bus changes upon closure of any key switch. The radio frequency is amplified and 1 applied to a rectifier to produce a DC potential proportional to the level of the radio frequency, and this is applied through a capacitor to a utilization circuit. Hence as the DC level changes through the capacitor, it appears as a pulse or spike at the utilization circuit, and this pulse or spike is used to key rhythm or other accompaniment effects.

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" sum, 2 BF 3 Ant/2022 CJ- 01410 RADIO FREQUENCY KEYING PULSE IN ELECTRONIC ORGAN The use of rhythm effects in electronic organs has become quite popular. Specifically, a brush or cymbal or other percussive efiect is played coincidentally with the playing of a note of the music being played. Various schemes have been developed for keying the rhythm effects in proper timed relation with the playing of a note, see for example Joseph H. Heme US. Pat. No. 3,3l7,649 and Harold O. Schwartz and Peter E. Maher US. Pat. No. 3,340,344. Typically, such key ing systems have utilized semiconductor devices, such as diodes, to convey the signal, the semiconductor devices being normally off and keyed on upon application of a keying potential from the bus rod. The keying potential is DC, and the bus rod is connected in a voltage divider circuit with the resistances of the key switches producing a progressive drop in voltage upon closing of one or more key switches. The bus rod is connected to a utilization circuit through a capacitor, whereby the level changes in DC potential on the bus rod are transmitted as pulses or spikes. The pulse or spike is used tokey the rhythm effects, whether it be drum, cymbal, etc. Such systems have worked quite well, but have been relatively expensive, due to the necessity of utilizing the semiconductor devices for keying.

As is well known, the least expensive keying in electronic organs is direct audio keying. That is to say, an audio frequency signal is applied to one side of a simple single-pole switch, and the output circuitry is connected to the other side of the switch. Upon closing of the key switch, the audio or musical tone signal is carried by the contacts of the switch to the output circuits. Heretofore, to the best of our knowledge, it has not been possible to key rhythm effects in connection with straight audio switching, other than through the use of additional switch contacts, thus increasing the cost.

In accordance with the present invention it is proposed to utilized direct audio keying of electric musical tone signals in combination with a radio frequency on the collector or bus rod. The radio frequency is applied through a resistor or impedance, operating in conjunction with impedances on the individual switch contacts to form a voltage divider. A radio frequency rejection filter is connected between the bus rod and the tone output circuits to prevent transmission of the radio frequency to the tone output circuits.

On the other hand, connection is made through a capacitor to an amplifier circuit, and from there to a detector circuit to provide a DC level proportionate to the radio frequency potential appearing on the bus bar. Since the radio frequency potential on the bus bar changes in accordance with the closing of a switch, and in accordance with the number of switches closed, the DC level likewise changes therewith. A capacitor is connected in the output circuit from the direct current potential, whereby the changes in DC level are transmitted as spikes or pulses which are used to key the audio effects.

Accordingly, the principal object of the present invention is to provide an electronic organ having straight audio keying wherein rhythm effects are keyed by the same key switch contacts as transmit the audio electric tone frequencies.

More particularly, it is an object of the present invention to apply radio frequency oscillations to a collector or bus bar in an audio frequency switching system of an electronic organ to develop pulses or spikes for keying rhythm effects.

Other and further objects and advantages of the present invention will be apparent from the following description when taken in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of an organ constructed in accordance with the present invention;

FIG. 2 is a block diagram illustrating the circuitry of the invention;

FIG. 3 is an electronic wiring diagram illustrating a simple embodiment of the invention;

FIG. 4 is an'electronic wiring diagram similar to FIG. 3 illustrating an improvement over the circuitry of FIG. 3;

FIG. 5 is a schematic diagram of a radio frequency oscillator as incorporated in the present invention;

FIG. 6 is an electronic wiring diagram of a modified oscillator circuit;

FIG. 7 is an electronic wiringdiagram similar to FIG. 6, incorporating also the radio frequency trap and output amplifier circuit; and

FIG. 8 is a fragmentary electronic wiring diagram illustrating a final commercial circuit including a plurality of bus bars.

Turning now to the drawings in greater detail, and first to FIG. 1, there will be seen an organ l0 constructed in accordance with the present invention, including the usual case 12 having a music rack 14 thereon. The organ includes a pair of keyboards 16, and is illustrated as being of the spinet type having a pair of overlapping, forshortened keyboards, although the principles of the invention are equally applicable to a full console organ. Various stop tablets and switches 18 are provided on the organ adjacent to the keyboard for selecting the voices and footages of the organ to be played, as well as the rhythm accompaniment effects. The organ also includes the usual pedal board 20, illustrated as being of the single octave plus one note variety, although it could equally well be a pedal board having 25 or 32 notes. A swell pedal 22 connected to an overall volume control likewise is provided in accordance with conventional practice. A speaker system 24 is housed behind grill cloth 26 on the front of the organ, and this may comprise a single speaker, or a plurality of speakers.

The electrical aspects of the invention will be readily understood with reference to the block diagram of FIG. 2. There is provided first a plurality of tone generators 28 individually connected through key switches 30 to a radio frequency or RF filter 32 leading to stops and tone filters 34. The latter is connected to an amplifier 36 for amplifying the electronic oscillations passed by the key switches, filters and stops, and the am plified oscillations are transduced by the speaker system 24. A radio frequency generator 38 also is connected to the key switches 30, and the radio frequency filter 32 blocks the radio frequency signal from the stops and tone filters 34, and hence from the amplifier and loudspeaker. However, a connection is made from the key switches 30 to a detector and shaper 40 which provides the desired DC pulses or spikes. These in turn are connected by way of a collector 42 and a plurality of stop switches 44 controlled by the stop tablets 18 to a like plurality of rhythm generators 46. As will be understood, the rhythm generators may be constantly operating, in which case the pulse will control a gate of some sort to effect passing of the rhythm signals. Alternatively, the rhythm generators can normally be quiescent, and be pulsed into operation upon closing of one of the switches 44. In any event, the output connections from the rhythm generators46 are made by way of a line 48 to the amplifier 36, and from thence on to the loudspeaker system 24. g l

A simple wiring diagram illustrating certain of the concepts enumerated with regard to FIG. 2, will be seen in FIG. 3. Thus, the tone generators 28, which operate at audio frequencies are respectively connected through resistors 50 to moveable switch contacts 52 which normally are positioned out of engagement with a bus bar 54. Only four such generators, re

sistors, and moveable switch contacts are shown, but it will be understood that for a normal spinet organ there will be 44 switches (and also generators and resistors) per keyboard, although this might in some instances be broken up into shorter bus bars.

The radio frequency generator 38 in the illustrative example produces 70 to volts peak-to-peak, and is connected through a capacitor 56 and a resistor 58 to the bus bar 54.

The output of the bus bar, illustrated as being at the right end, includes a radio frequency trap or elimination filter 60 including an inductor 62 and a capacitor 64 in series therewith. The radio frequency trap 60 is connected to a capacitor 66 leading to an amplifier stage 68. The amplifier stage includes is taken from the collector as indicated by the arrow 72, and

' positive voltage is applied through a resistor 74 to the collector, and also through a voltage divider resistor network 76 and 78 to the base, along with the input signal.- Thus, whatever audio frequencies of tone generators 28 are connected'to the bus bar 54 through the respective key switches 52, are passed by the radio frequency trap 60, and amplified by the amplifier stage 68. The amplified signals are transferred at 72 to the stops and tone filters, and are passed on the the amplifier and loudspeaker system. As will be understood, the radio frequency trap 60 prevents the radio frequency signal from appearing at the output 72.

On the other hand, the bus bar is also connected, as is indicated at the left end thereof, through a capacitor 80 and a series resistor 82, to a radio frequency transistor amplifier stage 84 including a NPN transistor 86 having the output taken from the emitter as indicated at 88, this being the well known emitter-follower circuit. The emitter is grounded through a resistor 90, and positive potential is applied to the collector through a resistor 92. A voltage divider network 94 and 96 biases the base of the transistor.

The radio frequency output appearing at 88 is applied to a diode 98, and specifically the anode thereof, the cathode being connected to a junction 100 which comprises the input of a smoothing RC filter comprising a shunt capacitor 102 and a resistor 104 in parallel therewith. The smooth or filtered DC is applied through a capacitor 106 to the output 42 discussed in connection with FIG. 2, the foregoing circuits comprising the detector and shaper 40 likewise discussed in connection with FIG. 2.

As will be apparent, the radio frequency potential appearing on the bus bar 54 with none of the moveable key switches 52 closed thereon is approximately the 70 to 80 volts peak-topeak developed by the radio frequency generator 38. Bearing in mind that both the radio frequency generator 38 and the audio frequency tone generators 28 are returned to the ground, upon closure of any moveable key switch 52 against the bus bar, there will be a radio frequency voltage divider network established comprising the resistor 58 and one of the resistors 50. Obviously, the capacitor 56 is essentially a short circuit or a direct connection relative to the radio frequency. Thus, the radio frequency potential on the bus bar 54 drops. If the first key switch contact 52 is held against the bus bar, and another key switch contact is moved against the bus bar, then there will be two resistors 50 in parallel, thus altering the voltage divider network, and dropping the radio frequency potential on the bus bar 54, bearing in mind the paralleling of the resistors 50 produces a lower resistance. This continues for the closing of any reasonable number of key switches (only five of which can be closed by the fingers of one hand).

It will be appreciated that the DC output potential from the amplifier stage 84 and diode 98 is directly proportional to the radio frequency potential on the bus bar 54. Thus,potential at 100 drops each time a key switch contact 52 is closed against the bus bar. Since the capacitor 106 does not transmit a DC potential, but will transmit the change in potential as a pulse, a pulse appears at 42 each time one of the key switch contacts 52 is closed against the bus bar 54. This pulse is used to pulse or key whichever of the rhythm generators has its input switch 44 closed, and thus to produce the rhythm accompaniment in the output loudspeaker system of the organ precisely on the beat as the musical tone is produced.

In the foregoing, it has been found that the peak-to-peak potential of the radio frequency generator must be at least five times the amplitude of the keyed audio signal, and this is about l4 volts. Thus, the radio frequency peak-to-peak voltage is on the order of 70 to 80 volts. The nominal 14 volts audio frequency drops to about 1 volt on keying, but the radio frequency remains at 80 volts. Hence, there is an 80 to 1 ratio, and there are no noise problems.

As will be appreciated, the radio frequency is quite far removed from the audio frequencies of the tone signals, and filtering to separate the two is no problem. Conversely, DC is close in frequency to audio frequency, and it is extremely difficult to eliminate clicks and pops.

The circuit of FIG. 3 was found to work well in practice, but certain improvements were made in connection with the circuit of FIG. 4. Most of FIG. 4 is identical with that of FIG. 3,

and hence similar numerals are used to identify similar parts.

At the upper right-hand corner a capacitor 108 is included in the output from the transistor amplifier stage 68. More significantly, there is no series resistor from the RF oscillator 38 leading to the bus bar 54, the capacitors 56 being the'only connection. Changes in RF level on the bus bar are produced by the internal impedance of the RF oscillator in connection with the resistors 50. Similarly, the resistor 82 is eliminated in the circuit to the transistor amplifier stage 84.

From the emitter output of the transistor amplifier stage 84, a series capacitor 110 and shunting resistor 112 are provided to the diode 98. From the diode 98 to the point 100 there is an additional filtering, comprising two series resistors 114 and 116, and a shunting capacitor 118. Furthermore, from the capacitor 106 there is an additional transistor amplifier stage and a further shunting capacitor 122 further to smooth the DC. A series capacitor 124 leads to a double transistor amplifier circuit 126 including NPN transistors 128 and 130, providing the output at 42 considerably amplified.

A typical RF oscillator circuit is shown in FIG. 5, including an NPN transistor 132. Positive potential is applied to the latter of the transistors through an inductor 134, for example of 27 mh. DC potential also is applied to the base through a divider network comprising resistors 136 and 138, for example respectively of 56K ohms and 2.2K ohms. The emitter is grounded through a resistor 140, for example of 2.2K ohms, and resistor is shunted by a capacitor 142, for example of 0.0002 mf. A feedback capacitor 144 is connected between the emitter and the top of the inductor 134, for example of 0.0005 mf. The output is taken through a capacitor 80 as previously indicated.

The radio frequency oscillator circuit is shown as slightly modified in FIG. 6, similar parts again being similarly numbered, the circuit being changed slightly, and the values likewise being changed to produce a nominal frequency of 90 kc, allowing a tolerance of i 10 percent, the RF trap likewise being tuned to 90. Thus, the emitter of the transistor 132 is returned not only to the top of the inductor 134, but also to the bottom thereof, and to the collector by a capacitor 146.

As to illustrative circuit values, inductor 134 is l0 mh. plus or minus 5 percent. Resistor 136 is 82K ohms and resistor 138 is 10K ohms. Resistor 140 is 2.2K ohms, while capacitor 144 is 1,200 pf., capacitor 146 is 330 pf., and capacitor 56 is 22 pf. With the applied voltage at 30 volts DC the circuit produces 80 volts peak-to-peak at 90 kc.

Turning now to FIG. 7, the RF oscillator 38 is the same as just described in connection with the FIG. 3, except that it operates at 15 volts, and for the fact that a diode 148 is connected between the resistor 140 and ground, the cathode of the diode being connected to ground and the anode to the resistor 140, and for the fact that a diode 150 is connected to the collector of the transistor 132. It is the cathode of the diode that is connected to the collector, while the anode is connected to the junction between the inductor 134 and the capacitor 146.

The diodes allow a greater peak-to-peak RF voltage to be developed as they prevent damage to the transistor by the back voltage. Although the two diodes lead to maximum peakto-peak voltage, one diode in the collector circuit provides for a sufficiently high operating voltage, and this is what is done in the commercial circuit of FIG. 8.

The applied potential in the circuit of FIG. 7 is plus 15 volts, and the radio frequency oscillation again is at 80 volts peakto-peak at 90 kc. The radio frequency trap remains as heretofore shown and described, and for illustrative purposes the inductor 62 is 10 mh. while the capacitor 64 is 390 pf. This produces 88kc. resonance with 49db. rejection.

FIG. 8 is provided as an illustration of a final commercial circuit embodying disclosures heretofore made. Thus, with reference to the upper left-hand corner of FIG. 8, there is an RF generator 28 substantially identical with that heretofore shown and described in connection with FIGS. 6 and 7. The

only difference is that the inductor 134 may be paralleled by a resistor 152 optionally selected to produce the proper frequency of oscillation. The diode 150 of FIG. 7 is incorporated, but the diode of 148 is not.

The output of the single radio frequency oscillator is connected to three different bus rods indicated at 54a, 54b and 54c. These may be segments of bus rods in the same manual of the organ, but more typically will comprise bus rods in the upper and lower manual and in the pedal board. The three circuits associated with the respective bus rods are similar to those previously shown and described, and are identical with one another, similar parts in the three circuits being identified with the same numerals as heretofore used, with the respective addition of the suffixes a, b and 0. ln addition each of the radio frequencies traps as 60.4, is provided'with a resistor 1540 in series with the capacitor 64a to lower the Q of the circuit, and thus to broaden the rejection band. Furthennore, each resistor 76, for example, 76a, is paralleled by a capacitor 156a being exemplary to roll off any RF that might pass the trap. The output of each of the three circuits as taken respectively at 72a, 72b and 720 is individually connected to the stops and tone filters 34 leading to the amplifier and from thence to the loudspeaker 24. y

In addition, each stop rod is connected, respectively by capacitors 80a, 80b and 80c, to the input of the detector and shaper 40, which is to all intents and purposes identical with that previously described in connection with FIG. 4, the output again being taken at 42 and applied to the respective rhythm generators 46, the rhythm oscillations being applied at 48 to the amplifier 36 as heretofore.

Thus, at relatively little expense, comprising the addition of only the RF oscillator, the RF trap, and the RF detector and shaper, we have provided means for producing pulses for keying rhythm generators in conjunction with straight audio keying in an electronic organ. As will be appreciated, there is just one of the RF circuits, and one RF trap per stop rod, hence obviating the necessity of duplication or multiplication of parts, and holding costs within practical reason.

Specific examples of the invention have been described with a radio frequency signal in connection with direct audio keying to produce a pulse for keying rhythm generators. However, it will be understood by those skilled in the art that a pulse could equally well be produced from RF with DC keying, i.e. the use of DC to turn on diodes or other electronic gates. Furthermore, the pulse developed could be used for purposes other than keying rhythm generators.

We claim:

1. An electronic keyboard musical instrument such as an organ having a plurality of manually operable playing keys, comprising means for providing audio frequency oscillations corresponding to musical tones, a plurality of key switches respectively operable by said keys and respectively connected to said tone generators, output means connected to said key switches for amplifying the oscillations from said audiofrequency-producing means and for converting the same to audible musical tones, rhythm accompaniment means normally inoperative to provide an output, means for providing radio frequency oscillations, means connecting said radio frequency oscillation providing means to said key switches, means operable as an incident to closure of any of said key switches to produce a control potential from said radio frequency oscillations, and means connecting said control potential producing means and said rhythm accompaniment means to render the latter operative to provide rhythm accompaniment to the musical tones of said output means.

2. A musical instrument as set forth in claim 1 wherein each of said key switches comprises a single-pole, single-throw switch.

3. A musical'instrument as set forth in claim 1 wherein said output means includes a radio frequency trap.

4. A musical instrument as set forth in claim 1' wherein the potential of the radio frequency oscillations are on the order of five times the potential of the audio frequency oscillations.

5. A musical instrument as set forth in claim 1 wherein the control potential comprises a pulse.

6. A musical instrument as set forth in claim 1 wherein the means providing the control potential includes means for rectifying the radio frequency oscillations to provide a DC potential.

7. A musical instrument as set forth in claim 6 wherein the control potential comprises a pulse.

8. A musical instrument as set forth in claim 1 wherein the means for producing a control potential comprises means for changing the level of radio frequency oscillations upon closure of a key switch.

9. A musical instrument as set forth in claim 8 wherein the means for producing a control pulse comprises means for producing successively different levels of radio frequency oscillation upon closing of successive key switches with prior key switches held closed.

10. A musical instrument as set forth in claim 8 wherein the means for changing the level of radio frequency oscillations comprises voltage divider means.

11. A musical instrument as set forth in claim 8 wherein the means for producing acontrol potential comprises means for rectifying the RF oscillations to provide a DC potential changing in level upon closure of a key switch.

7 12. A musical instrument as set forth in claim 11 and further including a capacitor to convert the changes in DC level to pulses.

13. A musical instrument as set forth in claim 11 wherein the means for providing a control potential comprises means for producing successive changes in RF oscillation level upon closure of successive key switches with a first key switch held closed.

14. An electronic keyboard musical instrument such as an organ having a plurality of manually operable playing keys comprising means for providing audio frequency oscillations corresponding to musical tones, a plurality of key switches respectively operated by said keys and respectively connected to said tone generators, output means connected to said key switches for amplification of the oscillations from said generators and for converting the same to audible musical tones, rhythm accompaniment means normally inoperative to provide an output, means providing radio frequency oscillations, means connecting said radio frequency oscillation providing means to said key switches, means operable at an incident to closure of any of said key switches to produce a change in level of said radio frequency oscillations, rectifier means connected to said last-mentioned means to produce a DC control potential changing in level upon closure of any key switch, and a capacitor connecting the rectifier means to said rhythm accompaniment means to produce a pulse to said rhythm accompaniment means to render the same operative to produce rhythm accompaniment to the musical tones to said output means.

15. A musical instrument as set forth in claim 14 wherein the means for changing the level of radio frequency oscillations upon closure of the key switch includes means for producing successive changes in level upon closure of successive key switches with an initial key switch held closed.

16. A musical instrument as set forth in claim 14 wherein the means for changing the radio frequency oscillation level comprises voltage divider means.

17. A musical instrument as set forth in claim 14 wherein each key switch comprises a single-pole, single-throw switch.

18. An electronic keyboard musical instrument such as an organ having a plurality of manually operable playing keys, comprising means for providing audio frequency oscillations corresponding to musical tones, a plurality of key-switching circuits respectively controlled by said keys and respectively interconnected to said tone generators, output means connected to said key switching circuits for amplifying the oscillations from said oscillation-producing means and for converting the same to audible musical tones, means for providing radio frequency oscillations, means connecting said radio frequency producing means to said key switching circuits, and means connected to and operable as anincident to operation of any of said key switching circuits to produce a control potential from said radio frequency oscillations.

19. A musical instrument as set forth in claim 18 wherein the control potential producing means comprises means for producing a pulse.

20. A musical instrument as set forth in claim 18 wherein the control potential producing means comprises rectifier means for producing a DC control potential. 

1. An electronic keyboard musical instrument such as an organ having a plurality of manually operable playing keys, comprising means for providing audio frequency oscillations corresponding to musical tones, a plurality of key switches respectively operable by said keys and respectively connected to said tone generators, output means connected to said key switches for amplifying the oscillations from said audio-frequency-producing means and for converting the same to audible musical tones, rhythm accompaniment means normally inoperative to provide an output, means for providing radio frequency oscillations, means connecting said radio frequency oscillation providing means to said key switches, means operable as an incident to closure of any of said key switches to produce a control potential from said radio frequency oscillations, and means connecting said control potential producing means and said rhythm accompaniment means to render the latter operative to provide rhythm accompaniment to the musical tones of said output means.
 2. A musical instrument as set forth in claim 1 wherein each of said key switches comprises a single-pole, single-throw switch.
 3. A musical instrument as set forth in claim 1 wherein said output means includes a radio frequency trap.
 4. A musical instrument as set forth in claim 1 wherein the potential of the radio frequency oscillations are on the order of five times the potential of the audio frequency oscillations.
 5. A musical instrument as set forth in claim 1 wherein the control potential comprises a pulse.
 6. A musical instrument as set forth in claim 1 wherein the means providing the control potential includes means for rectifying the radio frequency oscillations to provide a DC potential.
 7. A musical instrument as set forth in claim 6 wherein the control potential comprises a pulse.
 8. A musical instrument as set forth in claim 1 wherein the means for producing a control potential comprises means for changing the level of radio frequency oscillations upon closure of a key switch.
 9. A musical instrument as set forth in claim 8 wherein the means for producing a control pulse comprises means for producing successively different levels of radio frequency oscillation upon closing of successive key switches with prior key swiTches held closed.
 10. A musical instrument as set forth in claim 8 wherein the means for changing the level of radio frequency oscillations comprises voltage divider means.
 11. A musical instrument as set forth in claim 8 wherein the means for producing a control potential comprises means for rectifying the RF oscillations to provide a DC potential changing in level upon closure of a key switch.
 12. A musical instrument as set forth in claim 11 and further including a capacitor to convert the changes in DC level to pulses.
 13. A musical instrument as set forth in claim 11 wherein the means for providing a control potential comprises means for producing successive changes in RF oscillation level upon closure of successive key switches with a first key switch held closed.
 14. An electronic keyboard musical instrument such as an organ having a plurality of manually operable playing keys comprising means for providing audio frequency oscillations corresponding to musical tones, a plurality of key switches respectively operated by said keys and respectively connected to said tone generators, output means connected to said key switches for amplification of the oscillations from said generators and for converting the same to audible musical tones, rhythm accompaniment means normally inoperative to provide an output, means providing radio frequency oscillations, means connecting said radio frequency oscillation providing means to said key switches, means operable at an incident to closure of any of said key switches to produce a change in level of said radio frequency oscillations, rectifier means connected to said last-mentioned means to produce a DC control potential changing in level upon closure of any key switch, and a capacitor connecting the rectifier means to said rhythm accompaniment means to produce a pulse to said rhythm accompaniment means to render the same operative to produce rhythm accompaniment to the musical tones to said output means.
 15. A musical instrument as set forth in claim 14 wherein the means for changing the level of radio frequency oscillations upon closure of the key switch includes means for producing successive changes in level upon closure of successive key switches with an initial key switch held closed.
 16. A musical instrument as set forth in claim 14 wherein the means for changing the radio frequency oscillation level comprises voltage divider means.
 17. A musical instrument as set forth in claim 14 wherein each key switch comprises a single-pole, single-throw switch.
 18. An electronic keyboard musical instrument such as an organ having a plurality of manually operable playing keys, comprising means for providing audio frequency oscillations corresponding to musical tones, a plurality of key-switching circuits respectively controlled by said keys and respectively interconnected to said tone generators, output means connected to said key switching circuits for amplifying the oscillations from said oscillation-producing means and for converting the same to audible musical tones, means for providing radio frequency oscillations, means connecting said radio frequency producing means to said key switching circuits, and means connected to and operable as an incident to operation of any of said key switching circuits to produce a control potential from said radio frequency oscillations.
 19. A musical instrument as set forth in claim 18 wherein the control potential producing means comprises means for producing a pulse.
 20. A musical instrument as set forth in claim 18 wherein the control potential producing means comprises rectifier means for producing a DC control potential.
 21. A musical instrument as set forth in claim 20 wherein the control-potential-producing means comprises means for producing a pulse.
 22. A musical instrument as set forth in claim 18 and further including rhythm accompaniment means normally inoperative to produce an output, and means connecting said control-potentIal-producing means and said rhythm accompaniment means to render the latter operative to provide rhythm accompaniment to the musical tones of said output means. 